There are known commercial and military aircrafts (ATR, C295, A400M etc. . . . ) powered with engine that contains external rotating blades, called propellers, located on the wing. In other cases (CBA vector 123, SARA, AVANTI) such engines are located on the rear part of the aircraft.
One of the problems raised by engines with rotating external blades when installed on the aircraft is related to failure events such as a Blade Release event (i.e. an event where a external blade of one of the engines comes off and hits the fuselage), an Uncontained Engine Rotor Failure event (i.e. an event where a part of the internal rotors of the engine brakes, it is released and hits the fuselage that can also occur on the conventional turbofan engines were the fan blades are not external but ducted inside a fan cowl) or an event where other high energy engine debris is released and hits the fuselage.
These events can generate large damages where considerable zones of the fuselage structure are removed and could lead to a hazardous situation for the safety of the aircraft.
The certification requirement are very restrictive regarding safety of such events and they can drive the design of the fuselage that shall resist such damage events and guarantee the continuation of safe flight and safe landing without leading to a catastrophic accident (i.e. the fuselage shall be an impact resistant and tolerant to large damages).
When there is a failure of the engine high energy debris can be released and impact the fuselage. The fuselage needs to sustain such impact but also needs to sustain the loads that appear afterwards with the reduced strength of the structure after the damage is produced. Those loads are generated on the continuation of safe flight and landing mission to the closest airport (the so called “get home mission”).
One characteristic load case of this “get home mission” is a consequence of the failure in the engine. In this emergency condition, the aircraft operates with only one engine generating a forward thrust outside the plane of symmetry of the airplane. This thrust causes a yawing moment which must be balanced with a side aerodynamic force caused by the vertical tail plane of the empennage, so that the aircraft can continue flying in a controlled safe manner. As the vertical tail plane is located on the rear part of the aircraft, above the rear fuselage, this side aerodynamic force generates an important torsion along the rear fuselage.
This increase of torsional load becomes particularly critical when the damages occur on the rear fuselage structure as is the case when the engines are installed on the rear of the aircraft. These loads must be sustained by a fuselage for which a torsion strength is considerably reduced because a resistant section of the fuselage formed by an intact closed section which is very effective on torsional loads, may be damaged and is now an open section with a very reduced torsional strength.
In the case that engines are installed on the wing, the damages can occur on the central fuselage in front of the wing. In this area of the fuselage, the situation can be also dangerous, although not as critical as when the engines are installed in the rear part because there is no torsional load increase coming from the empennage.
Other loads that also appears on the “get home mission” come from the maneuvers, the gusts and the inertia that also impose an important bending and torsion moments on the fuselage sections.
A similar situation arises when the aircraft is submitted to damages caused by impacts of other high energy discrete sources such as a released ice formed on the engine blades or a released fragment of the aircraft as for example a trap or a tire debris.
A similar situation also arises when an external object hits the fuselage with high energy as for example in the case of a bird strike, a severe in fight hail impact or even a ballistic projectile impact.
These events can generate also “large damages” on specific fuselage sections, where a considerable area of the fuselage structure can be removed and could lead also to a hazardous situation for the safety of the aircraft.
As is well known, weight is a fundamental aspect in the aeronautic industry and therefore there is the current trend to use discrete reinforced structures with lightening discontinuities instead of continuous structure without possibilities for optimized weight penalty, and particularly to use structures of a composite material instead of metallic material even for primary structures.
The composite materials that are most used in the aeronautical industry consist of fibers or fiber bundles embedded in a matrix of thermosetting or thermoplastic resin, in the form of a preimpregnated or “prepreg” material. Its main advantages refer to:                Their high specific strength with respect to metallic materials. It is the strength/weight equation.        Their excellent behavior under fatigue loads.        The possibilities of structural optimization thanks to the anisotropy of the material and the possibility of combining fibers with different orientations, allowing the design of the elements with different mechanical properties adjusted to the different needs in terms of applied loads.        
The disadvantage of the composite materials compared to conventional light weight metallic materials like the aluminum, is its lower impact resistance and damage tolerance capabilities. No plasticity behavior as on metallic materials is present in composite material and they are not able to absorb high strain energy amounts when deforming.
There is therefore a need of fuselage structures made of composite materials capable to satisfy the above mentioned requirements.
WO 2009/068638 discloses an impact resistant fuselage made with composite materials comprising an outer skin and an inner skin, both skins being joined by means of radial elements configuring then a multi-cell structure providing the required torsional strength in the rear part of said aircrafts.
The present invention is also addressed to attend the aeronautical industry demand related to impact resistant and damage tolerant fuselages made of composite materials and propose a different solution than the one disclosed in WO 2009/068638.